Michael T. Collins, DVM, PhD and Elizabeth J.B. Manning, MPH, DVM
Department of Pathobiological Sciences
University of Wisconsin School of Veterinary Medicine
Why is it of interest to assess the global prevalence of Johne's disease? With agriculture, as with any aspect of modern life, neighbors' conditions affect one another. As the definition of "neighbor" is no longer limited to geographic proximity but includes those with whom we work and trade, unaffected by distance, it behooves us to appreciate circumstances beyond our borders.
In all likelihood, Johne's disease is to be found in every country. Being free of the disease is probably more a function of how hard one has looked than a true lack of incidence. Knowing that paratuberculosis is at least a potential if not actual concern for every country should promote a realistic, useful international perspective of the disease. A complete grasp of the extent of paratuberculosis will assist all those affected in the many ways possible by the disease, whether through regulatory activities, livestock management of medicine, research, and public health. This assistance will take the form of developing practical management, regulatory and economic policies. These policies, having been based on actual conditions, vs. abstract extrapolations, will support a uniform global arena for agricultural endeavors.
Specific realms to consider when assessing the international impact of Johne's disease include:
1. Trade barriers
As illustrated by the situation in Australia (see below), having M. paratuberculosis test positive herds can affect all aspects of trade. Prices can slide, demand drop, export regulations be required, etc. Additionally, dissimilar barriers between different countries can make trade more cumbersome and costly. In all probability, barriers will soon also address products made from animals with Johne's disease. These products currently are free of restrictions in all international markets.
2. Slowed global genetic improvement
Dissemination of genetically superior livestock can be hindered by the perception that the buyer is free of disease and the seller has some degree of prevalence. Actual genetic improvement will be prevented through the purchase, often with scarce resources, of untested and infected animals that then infect the recipient herd. Zoological parks exist on every continent. Johne's disease is a threat to the continued health and propagation of these rare collections.
3. Policies based on inconsistent testing methodologies
Conclusions based on interpretations of different tests applied in varying manners can be more expensive and unproductive than having made no conclusions at all. Testing methodology, results interpretation and the successes and failures in management application of test results should be shared among countries.
4. Costs (1,2)
The direct and indirect costs of Johne's disease stem from many realms. Losses with which we are most familiar include reduced milk production and weight loss due to poor feed conversion and clinical/subclinical disease, increased culling rate, time and labor both complying with and managing regulatory programs, testing expenses and research. An additional loss for developing nations is an impairment of economic development programs, as investments in livestock are wasted. Development of ecotourism programs (such as photo-safaris) can also be hampered by the threat of cross-infection between wildlife in national parks and surrounding domestic livestock. Impediments to tourism can curtail a major component of the GNP and the country's only source of foreign exchange.
The continued investigation of the possible association between Crohn's disease and M. paratuberculosis could benefit from a thorough global analysis of the incidence of both diseases.
6. Research and control
An assessment of the international prevalence of Johne's disease can help prioritize research efforts and funding, support the establishment of effective global disease control programs and better determine the cost-effectiveness of efforts intended to control and/or prevent the spread of paratuberculosis worldwide.
To gain an impression of the prevalence of Johne's disease internationally, a short survey was developed and faxed to a subset of the IAP membership. A literature review was conducted as well, and government publications were canvassed for any information pertaining to the disease.
It goes without saying that the topic of this paper, "the international perspective", is in fact a compilation of general impressions given the testing and interpretation difficulties inherent with Johne's disease. The most common impression received was the lack of information on any basis, be it local, national or international. As a Canadian respondent put it, "There is an amazing paucity of information n the prevalence of Johne's disease."
Given this "paucity", we will give a brief description of the world's exposure to Johne's disease. In most cases, the data is bimodal - either a country has it or it doesn't.
In countries of the African continent, testing for M. paratuberculosis runs the gamut from never being done to gene probe confirmation of BACTEC cultures. We were able to find information about 12% or 6 of the continent's 49 countries: Kenya, Nigeria, Sudan, Tunisia, Zambia and South Africa. (Only the Sudan and Kenya are contiguous, and that minimally: Kenya shares only 1/20th of Sudan's border.) In this case, "finding information" meant discovering that at least one case had been reported in recent years. In South Africa the disease has been reported in both sheep and cattle with a focus of isolated herds in the wetter regions of the country (Natal, E. Transvaal). The disease is believed to be neither highly prevalent nor of major significance in this country. In Zambia paratuberculosis is reported to be a greater problem in sheep than in cattle and Tunisia's reports dealt only with camels. No information has been found to date on the other 43 African countries, and therefore no conclusions can be drawn about Johne's disease prevalence in those areas.
New Zealand reports that paratuberculosis is widespread in dairy cattle and goats plus is of concern in sheep and beef cattle as well. The number of recorded infected dairy properties has jumped dramatically over the last 4 years, and it is believed that this registry of infected premises understates actual prevalence. In concert with an increase in the extent of the disease (also evidenced by a doubling in vaccine sales in a year), all research was stopped.
Each of the 7 Australian states manages and monitors its own agricultural activities. Of the 7, Johne's disease is endemic in one state, positive herds are found in two others (at a reported prevalence of 17% and 1.4%) and the remaining 4 states report themselves free of the disease. Sheep and cattle trade among the states is stymied, with demand, marketing and prices affected by the perception, as well as the certainty, of Johne's disease prevalence.
China, Japan, India, Korea, Kazakhstan, Nepal and the Philippines are countries in Asia with contemporary, albeit infrequent, reports of Johne's disease. Japan's information was the most extensive for the region, reporting an annual average of 212 cases of clinical bovine paratuberculosis over the last five years. These cases were confirmed at slaughter. As the United States government continues its efforts through USAID to develop dairy industries in Pacific Rim countries, the need for Johne's disease testing for the new industries should provide a sense of the prevalence in this region.
Incidence of Johne's disease is reported to be increasing in the Netherlands, Finland, Italy and Scotland. In other parts of the European continent, no change in incidence has been noted over recent years. Countries belonging to the constant incidence category are Norway, Denmark, Portugal and Belgium, France, Cyprus, the Czech Republic, Greece, Hungary, Iceland, Slovakia, Spain, Switzerland and Turkey report that cases of paratuberculosis have been found within their borders but offer no guess about the direction in which incidence is moving.
From 1989 to 1994, only seven cases of Johne's disease were identified. Found in six herds, they all were traced to imports from Denmark. A July 1994 publication stated that "Swedish livestock are free of paratuberculosis". In March 1995 however, a Swedish herd was found to be positive and was slaughtered. Seventy contact herds are now under investigation. Sweden's continued testing of its livestock after its having been deemed paratuberculosis-free was valuable.
We found information about only three countries in this region - Mexico and Brazil which report test positive cases and Argentina which believes incidence is increasing.
We close with another quotation from a survey respondent. "The incidence of Johne's disease appears to be increasing due to the veterinarian's interest and attention." With greater scrutiny comes increased appreciation of the extent of problem. We believe no region in the world is free of M. paratuberculosis infection in its ruminant livestock and that every region's agricultural sector therefore is hampered to some extent by Johne's disease. We also believe that the resources to address paratuberculosis-related problems on a state-wide and national basis will continue to shrink as financial constraints are felt in government and other sectors. More extensive pooling of resources and efforts on an international basis may be one of the few remaining ways of continuing efforts to improve diagnosis and management of this disease.
1. I.J. Gill. The economic impact of Johne's disease in cattle in Australia. Johne's Disease (proceedings) Milner, A. R and Wood, P.R. p. 36-40.
2. Jones, R.L. Review of the economic impact of Johne's disease in the United States. Johne's Disease (proceedings) Milner, A. R and Wood, P.R. p. 46-50.
3. R.J. Chiodini. The history of paratuberculosis (Johne's Disease) - A Review of the Literature 1985-1992. International Association for Paratuberculosis, Inc. 1993.
4. S.S. Bastianello and H.F. Huchzermeyer. Pathological, bacteriological and serological findings in 100 ewes and their fetuses from a paratuberculosis sheep flock in South Africa. Proceedings of the Fourth International Colloquium on paratuberculosis. Chiodini, Collins, Bassey.
5. Future Management of Johne's Disease in New Zealand. Ministry of Agriculture Regulatory Authority, Wellington. July 19, 1995.